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Putting the Brakes on the Immune System
from ScienceNOW Daily News
Your immune system protects you from bacteria and viruses, but you need specialized cells to protect you from your immune system. Overaggressive immune responses can cause everything from autoimmune diseases to organ rejection. Now, scientists have identified a new group of these specialized cells that seem to keep the immune system in check--at least in the short term.
The cells are a type of regulatory T cells, or Tregs. Researchers already know that Tregs serve as a mute button for the immune system. Last year, a team in the United States and another in Italy reported that infusions of Tregs forestall an often-fatal complication of bone marrow and stem cell transplants called graft-versus-host disease, in which immune cells in the transplant attack the recipient's cells. And several groups are planning clinical trials to determine whether Tregs curb the rejection of transplanted organs such as kidneys. To turn down the immune system, Tregs often latch onto a protein called TIM-3 on the surface of helper T cells--which orchestrate immune counterattacks against a pathogen--killing the helper T cell in the process.
Like the helper T cells they target, the newly identified Tregs have TIM-3 on their surface. Researchers led by transplant immunologist Terry Strom of Harvard Medical School in Boston found the new Tregs in abundance in mice that had recently received skin grafts. The cells gathered in the lymph nodes near the grafts and wriggled into the transplants themselves. In the culture dish, the TIM-3 sporting Tregs were better at shutting down immune cells than were ordinary Tregs, the researchers report online today in the Journal of Clinical Investigation.
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